This is a research study involving humans, of the interventional type with minimal risks and constraints (RIPH2). It is a multicentric, non randomized prospective study aiming to better understand the mechanisms of the response to anti-IL-23 biologics in Spondyloarthritis patients attending the rheumatology department of Cochin, Saint-Antoine, Henri-Mondor hospitals (APHP) and Maison-Blanche Hospital (Reims).

The aim of this project is to improve our understanding of the role of IL-23 in the pathophysiology of axial SpA and peripheral SpA.

This objective is detailed in three specific aims:

1. Define the effects of IL-23 on gene expression and cytokine production in innate and adaptive T lymphocytes from patients with SpA, and correlate them with the patient's genotype;
2. Phenotypically characterize immune cell populations in peripheral blood and in synovial fluid from peripheral SpA patients and identify at the single cell level the cells expressing the IL-23 receptor and/or producing IL-17.

The study population to be included are patients affected by SpA, attended to in the Rheumatology Departments of Cochin Hospital, Saint-Antoine Hospital Henri-Mondor hospitals in Paris (APHP) and Maison-Blanche Hospital in Reims. Participants will be divided into two groups: Group 1 comprises patients diagnosed with axial SpA, Group 2 SpA patients with peripheral SpA or psoriatic arthritis.

Inclusion Criteria:

• Age : Adults (>18 years)
• Satisfying ASAS diagnostic criteria for SpA
• Patient has active disease, defined by the presence of active synovitis, tendinitis, or dactylitis or significant inflammatory pain of the spine, judged by the examining clinician to be due to SpA.
• Informed consent signed
• Beneficiary of health insurance, except for the AME

Only for patients of Group 1 • Patient is naïve to biological therapies

Only for patients of Group 2

• Patient is affected by peripheral SpA (ASAS criteria) or psoriatic arthritis, with inflammation of peripheral joints
• Patient requires aspiration, as part of standard care

Non inclusion criteria:

• Patient is minor
• Patient is pregnant or breastfeeding
• Patient is immunocompromised
• Patient has received biological therapy with 2 or more biologics
• Patient is receiving corticosteroid treatment > 10 mg per day
• Patient is under legal protection, curators, guardianship
• Patient refuses consent
• Previous history of alcoholism, drug addiction, psychological problems, severe concomitant conditions that could invalidate the patient's consent or limit the patient's compliance to the treatment protocol.
• Beneficiary of the AME

Only for group 1

• Patient has received biological therapy